Characterization of Poly(N- (hydroxymethyl)methacrylamide-ATU) Hydrogels Synthesized by  Radiation Nurettin S ¸ ahiner, 1 O ¨ mu ¨rC ¸ elikbıc ¸ak, 1 Savas ¸ Malcı, 1 O ¨ mer Kantog ˇ lu, 2 Bekir Salih 1 1 Department of Chemistry, Hacettepe University, 06532 Ankara, Turkey 2 Ankara Nuclear Research Center, Turkish Atomic Energy Authority, 06983 Ankara, Turkey Received 18 February 2005; accepted 19 June 2005 DOI 10.1002/app.22462 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Poly(N-(hydroxymethyl)methacrylamide-1- allyl-2-thiourea), (poly(NHMMA-ATU)) hydrogels were synthesized by  radiation, using 60 Co  source at different radiation doses, to change the porosity and crosslinking density of the hydrogels. The percent of 1-allyl-2-thiourea (ATU) in the monomer mixture before the irradiation was varied between 2.5% and 10.0%, to increase the content of ATU, which was involved in some different applications in the hydrogels. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), elemental analy- sis, and the swelling experiments were used to characterize the poly(NHMMA-ATU) hydrogels synthesized in this study. Characterization results of hydrogels showed that crosslinking density of the hydrogels was increased by the increasing radiation dose and ATU content in the irradiated mixture. Swellability of these hydrogels was found to be high enough to allow the metal ions and biomolecules get- ting inside the hydrogels to interact with all active groups on/in the hydrogels in the adsorption applications. Equilib- rium swelling ratio of the hydrogels at pH 0.5 is at least half of the equilibrium swelling ratio of the hydrogels at pH 7.0. Oscillatory swelling behavior of poly(NHMMA-ATU) hy- drogels between pH 0.5 and pH 7.0 showed that the hydro- gels are quite stable at different pH conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1657–1664, 2006 Key words: N-(hydroxymethyl)methacrylamide; 1-allyl-2- thiourea; hydrogels; irradiation; swelling INTRODUCTION Chelating polymeric ligands have been extensively studied by several authors and many reviews are available in the field. 1–3 Recently, a great deal of inter- est has been observed in relation to the applicability of chelating agents for removal and separation of metal ions from heavy metal contaminated water and pre- concentration of precious metal ions from different samples. 4–6 Among many sorptive materials, various forms of synthetic polymers containing complexing molecules which are available at low cost have emerged as one of the most important matrices for the synthesis of new sorbents. 7–9 In the recent years, in- stead of chelating resins, some hydrogels having dif- ferent swelling ratio have been used for different ap- plications. 10,11 Hydrogels are special class of crosslinked polymers, and they can be prepared by different po- lymerization techniques. Using radiation technology, the polymerization procedure, the crosslinking struc- ture, and also the crosslinking density of the hydro- gels could be controlled easily. 12 Hydrogels are poly- meric networks, which absorb and retain large amounts of water. Hydrogels having different ioniz- able and hydrogen bonding capacity, show different swelling behavior in the solution at different pH, tem- perature, and ionic strength. These behaviors supply some advantages to the hydrogels in different appli- cations, especially in drug delivery systems. 13–15 Be- cause of their water-absorbing capacity, hydrogels are subject of investigation of researchers interested in fundamental aspects of swollen polymeric networks, and have also found widespread application in differ- ent technological areas, such as materials for contact lenses and protein separation, matrices for cell encap- sulation, removal of metal ions, adsorption of textile dyes, and devices for the controlled release of drugs and proteins. 16 –21 The advantages of the hydrogels are easy to obtain with some different polymerization techniques, and interacting species with the active functional group on/in to the polymeric sorbent could be penetrated inside cavities of hydrogel by the swellability of the hydrogels. Recently, there has been a substantial interest in the use of radiation- induced graft copolymerization of functionalized monomer onto polymeric hydrogels, for chelating sorbent materials. 22–25 In the present study, poly(N- (hydroxymethyl)methacrylamide-1-allyl-2-thio- Correspondence to: B. Salih (bekir@hacettepe.edu.br). Contract grant sponsor: Hacettepe University Scientific Re- search Foundation; contract grant number: HU 0302601007. Journal of Applied Polymer Science, Vol. 99, 1657–1664 (2006) © 2005 Wiley Periodicals, Inc.